LOANS - Summary of Total Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net deferred loan costs and fees	$ (199)	$ (170)
Total loans	2,372,436	1,129,064
Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,202,828	1,129,234
Net deferred loan costs and fees	(199)	(170)
Total loans	1,202,629	1,129,064
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,169,807
Net deferred loan costs and fees	0	0
Total loans	1,169,807	0
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	779,834	418,289
Commercial Real Estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	444,937	418,289
Total loans	444,937	418,289
Commercial Real Estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	334,897	0
Total loans	334,897	0
Commercial Real Estate | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	25,630	14,695
Commercial Real Estate | Construction and land development | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	8,315	14,695
Total loans	8,315	14,695
Commercial Real Estate | Construction and land development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	17,315	0
Total loans	17,315	0
Commercial Real Estate | Commercial real estate other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	754,204	403,594
Commercial Real Estate | Commercial real estate other | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	436,622	403,594
Total loans	436,622	403,594
Commercial Real Estate | Commercial real estate other | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	317,582	0
Total loans	317,582	0
Commercial and Industrial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	309,995	151,240
Commercial and Industrial Loans | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	184,186	151,240
Total loans	184,186	151,240
Commercial and Industrial Loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	125,809	0
Total loans	125,809	0
Commercial and Industrial Loans | Commercial other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	203,063	103,586
Commercial and Industrial Loans | Commercial other | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	120,302	103,586
Total loans	120,302	103,586
Commercial and Industrial Loans | Commercial other | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	82,761	0
Total loans	82,761	0
Commercial and Industrial Loans | Agricultural and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	33,264	31,808
Commercial and Industrial Loans | Agricultural and other loans to farmers | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	32,621	31,808
Total loans	32,621	31,808
Commercial and Industrial Loans | Agricultural and other loans to farmers | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	643	0
Total loans	643	0
Commercial and Industrial Loans | Tax exempt loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	73,668	15,846
Commercial and Industrial Loans | Tax exempt loans | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	31,263	15,846
Total loans	31,263	15,846
Commercial and Industrial Loans | Tax exempt loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	42,405	0
Total loans	42,405	0
Commercial Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,089,829	569,529
Commercial Loans | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	629,123	569,529
Total loans	629,123	569,529
Commercial Loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	460,706	0
Total loans	460,706
Residential Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,155,436	506,612
Residential Mortgages | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	518,556	506,612
Total loans	518,556	506,612
Residential Mortgages | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	636,880	0
Total loans	636,880
Residential Mortgages | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	1,155,436	506,612
Residential Mortgages | Residential real estate | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	518,556	506,612
Total loans	518,556	506,612
Residential Mortgages | Residential real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	636,880	0
Total loans	636,880
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	127,370	53,093
Consumer | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	55,149	53,093
Total loans	55,149	53,093
Consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	72,221	0
Total loans	72,221
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	116,392	46,921
Consumer | Home equity | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	48,018	46,921
Total loans	48,018	46,921
Consumer | Home equity | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	68,374	0
Total loans	68,374
Consumer | Consumer other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	10,978	6,172
Consumer | Consumer other | Business Activities Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	7,131	6,172
Total loans	7,131	6,172
Consumer | Consumer other | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans, gross	3,847	$ 0
Total loans	$ 3,847